I was watching a nature documentary where a crab produced several dozen babies, and then turned around and started eating them. If she needed the nutrients so badly, why not just have fewer kids? From a thermodynamic standpoint that would preserve more calories.
I’ve also seen footage of birds brooding, laying, and then hatching multiple eggs, only to push half of the chicks out of the nest. That’s such a huge investment of time and energy. Why not just lay fewer eggs?
In other situations it is more understandable: A male lion might kill another male’s offspring to make room for his own. Cuckoos push other baby birds out of the nest so they can be adopted by the parents. But many cases of infanticide in the wild just seem time-consuming and wasteful.
In: Biology
The parents need to produce enough young that *some* survive. The wild is a very unforgiving place and so mass production of young is required for the species to survive.
There are all sorts of stories about this. The two that come to mind is snakes that slip into unattended nests and eat everything in the nest. So that bird’s entire mating season is done in about ten minutes.
And then there is the time where a parent bird is trying to get all of its chicks fed and eventually one of them fails to thrive and dies. The parent does the utterly pragmatic thing: it breaks down the dead chick and feeds it to the remaining living ones.
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